2.2.3.1.2. Shared index

For some reasons having a multiple index copies on each instance can be costly, the shared index can be used.

This indexing strategy combines advantages of in-memory index along
with shared persistent index offering "near" real time search
capabilities. This means that newly added content is accessible via search
immediately. This strategy allows nodes to index data in their
own volatile (in-memory) indexes, but persistent indexes are managed by
single "coordinator" node only. Each cluster instance has a read access
for shared index to perform queries combining search results found in own
in-memory index also. Take into account that shared folder must be
configured in your system environment (for example: mounted NFS folder). However, this
strategy in some extremely rare cases may have a bit different volatile
indexes within cluster instances for a while. In a few seconds they will
be updated.

For both cluster-ready implementations JBoss Cache, JGroups and
Changes Filter values must be defined. Shared index requires some types of remote or shared file systems to be
attached in a system (for example, NFS and SMB).